1. Field of the Invention
The present invention relates to a data conversion apparatus for converting data, a data conversion method, and a recording apparatus including the data conversion apparatus.
2. Description of the Related Art
The needs of users who wish to print at high speed when recording onto a recording medium with a recording apparatus are increasing. When printing while emphasizing high speed, a method in which the number of passes is decreased during multipass printing, which is used to realize high image quality, is effective. Here, the expression “number of printing passes” is the number of cartridge scans required to complete one line.
Since the number of discharge ports of a recording head is a certain fixed value, the greater the number of passes, the more the paper feed amount for a single pass is decreased. On the other hand, the smaller the number of passes, the more the paper feed amount for a single pass can be increased. For example, if printing that is performed with two passes can be performed with one pass, a simple calculation shows that speed can be increased by a factor of two. More specifically, the lower the number of passes, the more the number of cartridge scans required for recording a given region (e.g., 1 sheet) can be decreased, and the larger the paper feed amount for a single pass becomes. As a result, the time required for printing one sheet can be shortened.
Printing is performed by scanning in a direction which is approximately perpendicular to the discharge port array direction with a recording head. The recording head has a plurality of discharge ports which discharge a recording liquid (ink). Accordingly, when printing is performed in one pass, from a single scan a belt-like image region (band) is formed.
Since a one band region is formed from a single scan when printing in this manner in one pass, the duty (percentage) of recording ink printed onto the recording medium from one scan is greater than multipass printing which forms a one band region from multiple scans. Therefore, in a case of one pass printing, the appearance of a black streak (stripe) between passes (between bands) in portions of high printing duty is notable although its degree varies depending on properties of the recording medium or the recording liquid.
This black streak appearance is more noticeable when head structures is configured such that a recording head which discharges a plurality of different recording inks (cyan, magenta, yellow etc.) is arranged in a main scanning direction, a so-called “lateral configuration”. This is because the joint (connecting) positions of the respective colors appear at the same place.
Such black streaks appearing at the boundary portion between adjacent bands are also called “joint streaks” and “banding” and “connecting stripe”. If a joint streak appears, print quality deteriorates.
Japanese Patent Application Laid-Open No. 11-188898 discusses a method which, when recording one band at a time and repeatedly scanning the recording head in a main scanning direction, prevents the appearance of streaks in the joint (connecting) portions of a recording region for each of those bands. This method divides at least either the first raster or the last raster in a one-band region to be recorded, into unit regions having a predefined dot number, and then thins-out the print data based on binary data of those regions. This thinning-out is performed in a predefined preferential order according to the total of the ink discharge amount of a target color and the discharge amount of the other inks, in each unit region. By thinning-out the data in this manner, the discharge amount of the target ink is decreased.
Further, an example of another thinning-out method is to count the dot number in a unit region and determine the thinning-out ratio from that result. Based on this thinning-out ratio, the data to be printed is subjected to thinning-out processing (refer to Japanese Patent Application Laid-Open No. 2002-96460).
Recently, the number of ink colors and the number of discharge ports of the respective ink colors mounted on the recording head have been increasing, which has resulted in an expansion in the amount of data being processed by the recording apparatus. Accordingly, for example, image data expressed as multivalued data (multivalued information) rather than binary data is input from a host apparatus. Therefore, the recording apparatus converts the multivalued data input in the apparatus into binary data, transfers that converted data to the recording head, and prints the data onto a recording medium.
In Japanese Patent Application Laid-Open No. 2002-96460, it is discussed to perform thinning-out processing when converting RGB multivalued data into CMYK multivalued data.
However, Japanese Patent Application Laid-Open No. 2002-96460 does not specifically discuss how to perform the thinning-out in a case of the multivalued data.
On the other hand, various types of data are input into a recording apparatus from the host apparatus. Examples of such data include binary data, multivalued data expressed as 2-bits, and multivalued data expressed as 4-bits. Thus, a recording apparatus into which various types of data are input needs to have a thinning-out processing circuit corresponding to the data types. In an apparatus having such a configuration, the scale of the thinning-out processing circuit increases as the more types of data are provided.